Yesterday I dist-upgraded my system (first in several months that took 40 minutes and added +/- 1/2 GB).
I didn't notice any (major) complaints.

After reboot, rather than my KDE-login appearing, came:
"Warning: cannot open ConsoleKit session: Unable to open session: the permission of the setuid helper is not correct."

Googling, I found lots of complaints, but nothing like a practical fix.

Before crying for help, I re-dist-upgraded.
A list of unmet dependencies showed, and advice to try:

Code:

apt-get -f install

I did that. The process ran to completion and returned to root prompt.
I rebooted. My system recycled. The ConsoleKit warning appeared again (momentarily), then disappeared. And my KDE login window appeared.
And everything appears to now be in order.
Gott sei dank.